The present invention relates to closure technology for plastics or plastics coated containers. It is applicable to plastics bottles and steel containers which have a plastics coating or containers made of composite materials with a sandwich construction having plastics surfaces with paper and EVOH or aluminium layers glued together between the plastics surfaces.
The invention is particularly applicable to carbonated and non-carbonated, pasteurised, aseptic or hot-fill products and more specifically to a process for assembling a plastics spout to such a container. The predominant plastics material for gas-tight and heat-resist plastics bottles suitable for this purpose is PET (polyethylene terephthalate).
PET bottles cannot be used for sterilisation by retorting or autoclaving as is used for cans, glass bottles and some high heat resistant plastics such as polypropylene, as they cannot withstand the long exposure to temperatures of the order of 120° C. that are involved.
However sterile packaging in such plastics bottles can be achieved by an aseptic process or by hot filling.
In aseptic filling a UHT process is used to process the product prior to filling. The product is subjected to high temperature (140° C.) for a very short period (4 seconds) and then cooled to a temperature between ambient and 4 degrees C. Once cooled the product must remain in sterile conditions and cannot be exposed to environmental air or bacteria. The bottles and caps must also be cleaned and sterilised, typically using Hydrogen Peroxide or Paracetic acid, which is evaporated off the components. The bottles are then filled and sealed in an aseptic environment. The packaging must also be sealed tightly enough to prevent re-infection. While this process is effective to provide long shelf-life products and can be used with PET bottles the cost of the filling plant is significant.
PET bottles are also used in hot filling processes in which the product is at a temperature of typically in excess of 85° C. as it enters the bottle. In this process the bottles must be clean but not necessarily sterile as any bacteria present will be killed by the hot product. Hot fill processes are more economic but their applications are restricted by the limited heat resistance of PET, which suffers distortion at temperatures over 75° C. Greater than normal heat resistance can be obtained by crystallizing a neck of the bottle, but this increases the cost of the packaging.
A further technical problem is encountered when PET bottles are used in hot filling because a partial vacuum is created inside the bottle after it has been sealed as the product cools. This makes it necessary to develop constructions that prevent collapsing of the container. Examples of such structures are described in WO0113407 and WO0112531 in the name of Graham Packaging Company L P.
An injection stretch blow-moulded PET bottle will normally be sealed by means of an injection moulded cap which engages with features injection moulded on a neck of a preform prior to stretch blow-moulding into a bottle. This will result in good sealing characteristics if the neck remains as originally moulded but begins to fail if there is distortion during the hot filling process. Since a tight seal is essential to prevent re-infection this limits the scope for using PET bottles in the more economical hot filling process although this problem can be overcome by the use of a neck containing more material or by crystallization. These solutions increase the cost of the packaging. The present invention aims to solve this technical problem by the use of alternative closure technology.
An injection moulded spout with a cap has been described in WO 99/61337 (Spreckelsen McGeough Ltd). This type of closure technology has been applied to extrusion blow moulded bottles where the bottle body and the spout and cap could be made of the same material, typically high density polyethylene (HDPE). Such a material has a typical melting point of 140° C. In this closure technology the bottle and spout are sealed together by means of an intervening plastics coated foil which is welded to both surfaces. The spout and cap assembly is applied to a bottle body after filling and would therefore not be affected by the passage of the hot filled product during hot filling. Technical problems are encountered if such a closure assembly is applied to a PET bottle.
The first technical problem relates to the distortion of a pourer part of the spout when it is subjected to temperatures sufficient to weld the foil to PET, which only melts at 220° C. although some distortion will occur at lower temperatures. It is not practicable to make the spout from PET as this material is too brittle for injection moulding a component of this type.
A second technical problem of low weld strength arises if lower temperatures are used to produce the weld between the plastics coated foil and the PET bottle. This may result in a weld which is not strong enough to hold in the pressure of a carbonated product. If the weld joining the spout to the bottle body is weak it may be possible to remove the spout at this junction by applying a lever under a skirt of the spout and using a transport ring of the bottle as a pivot support. This undermines the use of the foil to provide tamper evidence.
Prior art proposals such as described in GB-A-2108464 (Container Corporation of America) suggest welding a foil onto an upper flat top surface of a container.
Unfortunately, this proposal would create a third technical problem if used with PET containers because of the weakness of the weld strength as described above.